1. Field of the Invention
The present invention relates to control valves for hydraulic elevators.
2. Brief Description of the Prior Art
A conventional hydraulic elevator control valve is provided with a main hydraulic channel through which the main flow of hydraulic fluid passes; a movable speed regulating plug disposed in the flow of hydraulic fluid; and a system of secondary hydraulic channels, which are connected to each end of the speed regulating plug, and which communicate with the main hydraulic channel, such that, when the control valve is closing, one flow component of hydraulic fluid flows out of the space at one end of the speed regulating plug, and a second flow component flows through a throttle and then into the space at the other end of the speed regulating plug. The speed regulating plug thus moves with the flow of hydraulic fluid, and the position of the speed regulating plug determines the rate of flow of the hydraulic fluid into the actuating cylinder of the elevator, thereby controlling the speed of the elevator.
The viscosity of oil, which is the hydraulic fluid most commonly used in hydraulic elevators, is reduced by about a decade as the oil is heated from the lowest working temperature to the highest working temperature. In the case of an elevator provided with a pressure-controlled ON- OFF-type control valve, this has the effect of producing an increase in deceleration with an increase in temperature, because the reduced kinetic resistance to movement of the valve plug, offered by the oil, allows the control valve to close faster.
In principle, deceleration of the elevator is based on a hydromechanical time reference. After the supply of electricity to the magnetic valve has been interrupted, a spring pushes the speed regulating plug of the control valve towards the closed position, while a throttle in the secondary hydraulic circuit supplying the speed regulating plug retards the closing of the valve. It is important to notice that the closing speed depends on the viscosity of the oil even in the case of a fully viscosity-independent throttle, because the kinetic resistance to movement of &:he speed regulating plug depends on the oil viscosity. As the kinetic resistance diminishes in response to reduced viscosity, the pressure difference across the throttle increases, producing an increase in the rate of flow in the secondary channel, towards the speed regulating plug, and therefore an increase in the plug speed.
A problem in this case is that the elevator, when working at "normal operating temperature", has an excessively long creeping time when arriving at a landing. This is because the distance at which the deceleration vanes in the hoistway are spaced from the landing must be adjusted for the lowest oil temperature to avoid overtravel.
German patent application publication DE 2908020 proposes a device for decelerating a hydraulic elevator by means of throttles and valves controlling the open position of the by-pass valve. The adjustment depends on the temperature of the hydraulic fluid. However, the device has the disadvantage that it uses a magnetic valve, necessitating a connection to the electrical system, thus rendering the solution too complex.